In response to the consumers' demands for compact electronic devices, all the electronic elements for the electronic devices must also be reduced in size. However, heat generated by the size-reduced electronic elements forms a main hindrance to the good performance of the compact electronic devices. Nevertheless, consumers still demand for enhanced performance of the electronic devices even if the semiconductors forming the electronic elements are constantly reduced in size.
A size-reduced semiconductor element would have increased heat flux. With the increased heat flux, it becomes more difficult to overcome the problem of cooling an electronic device. The increase of heat flux would cause overheat of the electronic device at different time and over different length or size of the device, and might cause damage to or even burnout of the whole electronic device.
A vapor chamber is applied to transfer heat between two relatively large faces, and is therefore different from a heat pipe that transfers heat between two points. And, the vapor chamber can be advantageously used in a relatively narrow space.
The vapor chamber has a heat absorption face and an opposite condensing face, and internally defines a vacuum space having a working fluid filled therein. The vacuum space is internally provided with a plurality of supports and a wick structure. The supports are respectively connected at two ends to the heat absorption face and condensing face for supporting the vacuum space. The heat absorption face of the vapor chamber is in contact with a heat source while the condensing face is connected to another heat dissipation device, so that heat absorbed by the working fluid is further transferred to the another dissipation device and dissipates into external environment therefrom. The working fluid absorbs heat from the heat absorption face and is therefore vaporized. The vapor-phase working fluid flows in the vacuum space to the condensing face and condenses into liquid again when contacting with the condensing face. The liquid-phase working fluid flows back toward the heat absorption face due to a capillary effect of the wick structure in the vacuum space to thereby complete one cycle of liquid-vapor circulation in the vapor chamber to transfer heat.
The conventional vapor chamber is used with a circuit board, so that heat generated by heat-generating elements on the circuit board is transferred to the vapor chamber and is finally dissipated into ambient air from the condensing face of the vapor chamber. To connect the vapor chamber to the circuit board, an internally threaded hollow copper post is extended through each of four corners of the vapor chamber without interfering with the vacuum space, and holes are formed on the circuit board at a positions corresponding to the copper posts, so that fastening elements can be screwed through the copper posts and the holes to lock the vapor chamber to the circuit board. To avoid interfering with the vacuum space, the copper posts are provided at four corners of the vapor chamber to locate relatively distant from the heat-generating elements. As a result, the heat absorption face of the vapor chamber is not in tight contact with the heat source and there is a thermal resistance between the vapor chamber and the heat-generating elements. To overcome the above problems, there are manufacturers who try to provide the copper posts on the vapor chamber at positions near the heat-generating elements. That is, the copper posts are directly extended through the vacuum space of the vapor chamber. In this manner, the vapor chamber can be in tight contact with the heat source to prevent the thermal resistance. However, the vacuum space being extended through by the copper posts loses its vacuum tightness and is no longer in a vacuum state. Further, the copper posts extended through the vacuum space would inevitably form an impediment in the flow path of the working fluid filled in the vacuum space to thereby cause reduction in the heat transfer efficiency of the vapor chamber. In some worse conditions, the working fluid might leak out of the vacuum space to result in a useless vapor chamber. In brief, the vapor chamber with the conventional mounting structure is subjected to the following problems: (1) there would be a thermal resistance between the vapor chamber and the heat source; and (2) the vapor chamber might have reduced heat transfer efficiency.